Portable fluid heaters for rapidly heating large volumes of water or other fluids are required for certain applications. Such applications include the heating of hydrocarbon well fracturing fluids, which are generally aqueous fluids that are typically heated to about 15° C.-50° C. and mixed with proppants and surfactants before being injected into a hydrocarbon well. Portable heaters for this application must be lightweight, rugged, efficient and capable of high heat output.
FIG. 1 is a schematic side elevational view of an exemplary portable fluid heater 20. The portable fluid heater 20 combusts fuel supplied from fuel tanks 22, 24 to heat cold fluid pumped in through inlet 26. The cold fluid is circulated through a fluid path within the portable fluid heater 20 and adsorbs heat from the fuel consumed. The heated fluid exits through a fluid outlet 28 and is stored in a holding tank (not shown) or is piped directly to a blender (not shown) where the proppants and/or other additives are mixed with the heated fluid before it is injected into a well.
Many configurations for portable fluid heaters are known, but almost all of them discharge large volumes of hot flue gas 30 into the atmosphere. Regardless of how efficiently portable heaters combust fuel, sensible and latent heat in the flue gas is not utilized. There therefore exists a need for a condensing heat recovery unit for portable fluid heaters to utilize at least a part of that wasted heat.